Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$64.96	10.710%	$71.9172	$71.92	$71.90	$71.90
Purchase #2	$146.74	8.718%	$159.5328	$159.53	$159.55	$159.50
Purchase #3	$169.90	5.595%	$179.4059	$179.41	$179.40	$179.40
Purchase #4	$77.98	10.854%	$86.4439	$86.44	$86.45	$86.40
Purchase #5	$48.95	5.195%	$51.493	$51.49	$51.50	$51.50
Purchase #6	$32.66	7.678%	$35.1676	$35.17	$35.15	$35.20
Purchase #7	$43.44	6.793%	$46.3909	$46.39	$46.40	$46.40
7 purchase totals =	$584.63		$630.3513	$630.35	$630.35	$630.30